1. Field of the Invention
The present invention relates to an image pickup apparatus, such as a digital still or video camera, that compresses digital image data and records the compressed image data to a recording medium.
2. Related Background Art
Conventionally, a digital camera is generally known wherein the image of an object acquired through an image pickup lens is photoelectrically converted with an image pickup element such as a CCD, and A/D conversion is performed on the obtained image signal to record the resultant image data onto a recording medium. In this camera, image data is temporarily stored in a buffer memory, and thereafter, are transferred to and stored into an external recording medium, such as a compact flash (R) card (a CF card) or a hard disk, that is detachably attached to the main body of the camera.
Recently, for images obtained by a digital camera, the need has arisen for the improved image quality available with higher resolutions, and this has resulted in an increase in the number of pixels of an image pickup element. Accordingly, the image data volume has increased, and extending the data processing period, i.e., increasing the intervals for photographing and recording, has become a problem, and could cause a user to miss a good opportunity for a photograph.
To avoid such a problem, a camera has been proposed wherein when image data is obtained it is temporarily stored in a built-in buffer memory, and wherein when the next photographic instruction is received while the temporarily stored image data is being transferred to and recorded onto an external recording medium, the recording operation is halted so that to the maximum extent possible, the photographic process is performed preferentially in accordance with the remaining capacity of the buffer memory.
When the taking of a photograph has been completed, the recording onto the external storage medium of the temporarily stored image data is resumed. For this purpose, to notify a user that image data is being recorded, a camera is generally so designed that the recording of data onto the external recording medium is indicated by blinking an LED. Further, a camera in which a large buffer memory is mounted is superior because photographs can be taken quickly, at an opportune timing. Since an enormous amount of data are collectively transferred from the buffer memory to an external recording medium. the recording period may be extended. Therefore. during this recording period. the external recording medium and a power source battery must remain being attached; however, while the recording period is being extended. there is an increasing probability that the external recording medium or the power source battery will be carelessly and erroneously removed.
According to a digital camera disclosed in JP-A-2000-278577, while first priority is given to the photography operation and second priority is given to the recording operation, other operations, i.e., the switching off of a power switch and the image reproduction operation, are initiated after the data recording for an external recording medium has been completed. Further, when data is being stored in the buffer memory provided as the temporarily storage of image data, a reduction in the power source voltage or the sudden removal of an external recording medium or a battery generates an alarm to alert a user to the recording state of the external recording medium.
Further, as is disclosed in JP-A-2000-152139, a mechanism is provided that, when the camera is set in the photography-enabled state, the removal of an external recording medium is inhibited.
However, when the external recording medium or the battery is abruptly removed while the data in the buffer memory is being recorded onto the external recording medium, a data management file in the external recording medium is not recorded, and thus the image data that have been recorded can not be read out. Therefore, as is disclosed in JP-A-2000-278577, no problem will occur so long as the external recording medium is not removed or the battery power is maintained during a period after which the operation is shifted to one other than the photography. But even when an alarm is generated upon the removal of an external recording medium or a battery, it is then too late to protect recorded data, and further, when it is the battery that is removed, there is a high probability that data remaining in the buffer memory will be lost or data recorded onto the external recording medium will be destroyed.
However, since according to the camera disclosed in JP-A-2000-152139 a removal inhibition mechanism that operates synchronously with a turn-on power switch is required to prevent the negligent removal of an external recording medium, the manufacturing costs will be increased.
Therefore, the objectives of the present invention are the prevention of an increase in the manufacturing costs, and the improved maintenance of the image data recording condition, to ensure that image data temporarily stored in the internal memory of a camera are not lost due to a user error and to enable the later recording of data to an external recording medium.